Most of the complaints have come from Wellingtonians after new buses with bright blues lights onboard were rolled out. A spokesperson from Wellington's public transport network, Metlink, told Newshub the buses come equipped with the blue lighting and that customers have expressed both positive and negative comments.

But bus passengers in Wellington claim the blue lights have caused headaches and dizziness. One person said the last thing they want after a day staring at a computer screen is a bright blue light giving them a headache on their way home.

The Metlink spokesperson said the lights are installed by manufacturers as a safety feature because they reduce internal glare that could affect the driver's view. They have white lights too that come on when the bus doors open (as the video below shows).

But another passenger said on Twitter they're "really unsure" why the buses have "intense blue lights" when blue light is "commonly linked to headache pain" and "migraine triggers".

Auckland University's Dr Andrew Collins, a registered optometrist, told Newshub the main issue with blue light is that people can "find it quite glary" and that's because blue light "scatters more than other colours". If a person has cataracts, they can find it quite disturbing, he said.

"A number of manufacturers of electronics have added blue light filters that reduce the amount of blue light in the evening because blue light can certainly affect sleeping patterns. However, blue light in the morning is actually quite good because it helps you wake up, whereas blue light at night can delay the onset of sleep depending on the intensity."

Dr Collins said there is an argument that blue light at night could affect some peoples' sleep. But at the intensity of brightness on a regular bus, he said the risk of damage to peoples' eyes is low. He said it's much more likely that people would find it too glary and could get headaches.

The blue bus lights have garnered a range of responses from the public, with one person saying the new buses' neon glare reminds them of a disco. Even Newshub's Wellington-based political editor, Tova O'Brien, tweeted a response to the neon lights which she likened to a "glow stick".

The blue lights have also featured in some Auckland buses. Auckland Transport spokesperson James Ireland told Newshub Auckland Transport consulted bus drivers who were "keen" on the idea.

But blue lights are not part of the standards set by Auckland Transport, he said. The buses in Auckland are owned by individual companies like NZ Bus, Ritchies and Birkenhead Transport. Ritchies has a few buses with blue lighting on the top deck of double-deckers, and "that was their decision," said Mr Ireland.

He said he's not aware of any formal complaints made in Auckland about the neon lights being used on some buses, and dismissed a theory that the blue lights could have been introduced to stop drug users finding their veins to inject themselves, although he admits he has heard of the rumour.

While the blue lights may serve a safety purpose for bus drivers to reduce reflection on their front windscreens, Metlink has been criticised for not providing constructive responses to those who have spoken out on Twitter saying the light hurts their eyes and gives them headaches.

When Newshub approached Metlink for response about blue lights potentially causing sleep loss for passengers, the spokesperson said, "No issues of this nature have been brought to our notice, but people who have any such concerns would be best advised to seek the appropriate medical advice."